Manufacture of cellulose acetate



i Patented Nov. 3,

nanny nanrnus, or ilonnon, ENGLAlND mnaw g; orig flap uaaai filed April 18, 1923', Ser-ia1 1 Io.l633,016, and. in Great-Britain May 24,

MiiiANUFACTI RE on cnnnunosn smara i922. rimed and this application fiied aji ry'ao, 1 926.1 Serial no; 82,623. V r

" fThis application is a'division of the applic'cation-of Henry Dreyfus, SJQNo. 633,016 filed April 18, 1923 which has eventuated into Patent No. 1,708,787 on April 9,1929? This inventiongrelates to the manufacture of cellulose acetate, from celluloseoritsnear ,converswn roducts,'which latter are-herein- 7 after inclu ediunde-r the term cellulose,

In previous U. S; Patents Nos. 1,278,885

1,280,974 and "1,280,975 and British Patents 14,101 of 1915, 6,463 of 191'5, 1 01,555 and "100,009, I have described processesfor the manufacture of. celluloseacetates which are very viscous and produce very viscoussolu- 131011521 f f f v The present nvention aims'tomake new .cellulose acetates, which aremo're viscous thanithei products obtained according to my said patentsor'any known process, and capa bleof giving whether as primaryesterifiea- "ti'on' products orfproducts of further trans formation; stronger and better artificial silk great or more.-

'or other technicaliproducts than any here tofore. obtainable with fatty acid esters of cellulose. v

the weight of cellulose) has been' 'lsed asa solvent in the process'of acetylating cellulose.

"In these processes acetic 'anhydrideto the ex "tent of 1 to 6 times theweight ofthe'cellulose is used, the amount-of the acetic can'hy dride usually; varying inversely withthe amount of acetic acid used (usually the less acetic acid used the more anhydride) The applicant has discovered that the acetic acid plays an importantpart'in the production of very viscous products and does not serve merely as afsolvent ordiluent as i has hitherto been supposed. This is evidenced by the fact that the acetylation solution obtained by the applicants process'hereinafter described is at least as viscous as the acetylation solution obtained under otherwiselsirnilar conditions by.prio r' processes, although :the dilution may be at least2 to .3 'tirnes'as The applicant has 1 also retina th'at the quantity of acetic anhydride .taken" in "excess of that required for the ac etylation also plays p nt part:

'Hithe'rto acetic acid (about 4 to 6 times,

According to thepresentinventionthe ratio of acetic acidused'fin the acetylation or esterihcation 1s increased from the Customary about l to 6 parts of acetic acid to 1 part of cellulose" t0,ior example, to about 8 to 12 and a Q preferably even substantially more partsof acetic acid to lpartbf cellulose.

p This increase n the amount of acetic acldused. not

'uct but it enables the esterification to be m ore easilycontrolled and hindersthe depolyme'rization' ofthe cellulose molecule.

The use, of ,8 an increased. proportion of only results .in'a purer and more viscous prodacetic acid in conjunction with sulphuric acid or other strong condensing agents in the acetylation of celluloselfor'ms: the subject matter of' 'the parent specification S. No. 33,016; 4

' In accordance with the present invention,

the vigorous evolution of heat that takes 'place'when a strong condensingagentis used,

is avoided by the use in conjunction with an lncreased proportionof acetlc acld, as aforeagents, for example bisulphates containing small proportions of sulphuric acid as eX- plained in my U.:S;Patent 1,280,974 and my British 'Patent "100,009, or bisulpha'tes alone,

"said, of weak or' relatively weak condensing or sulphates like! aniline sulphate, or ammomum sulphate or ammonium bisulphate, or any otheriweak condens ng agent capable of promoting acetylation atan appropriate .tem-

perature.

. When weak condensing agents and especially small 'quantities of them, are used, quantities ofacetic "anhydride in excess of that neee'ssaryior the required acetylation can be used without danger of the destrucerts on'the cellulose in the presence of strong condensing agents like sulphuric acid;

, If,,for example, one takes any increased 'quantity of acetic acid, for instance 8times the weight of the cellulose,while not substanwhichare'just as viscous, in spite oftheir intive action. which excess acetic anhydride excreased dilution, as the solutions obtained with much less acetic acid, for eXample Only four times the Weight of the cellulose.-

The quantity of acetic acid is preferably increased to more than 8 times the weight of the cellulose, e. g. to 10 or 12 times and more as desired, products of increasedviscosity being thus obtained :or withless advantageless than8 times the weight relatively to the cellulose may be employed. r I H v Coupled with the use ofweak condensing agents, the dilution with acetic acidhas a further advantage in that the control ofjthe heat evolved by the reaction, whichis very great when sulphuric acid or strong condens ing agentsare used, is-much moreiin hand and can be regulated much-more 635113 When,

for the acetyl ation condensing agents are used which necessitate higherv temperatures for. the reaction, the'conditions haveto be adapted. Thus in the case of ammonium sulphate or sodium bisulphatetheapplication of heat becomes necessary.

.7 addition to amoreIetlicient temperature control, the use of anincreased amount of acetic acid also enables the hydration of the cellulose before the factual acetylation sets in to bejmore easily regulatedthis without atboiling point, according to the weakness of .tacking or substantially attacking the cellulose. V.

The increased dilution also permits a higher temperature to beused (although less adyantageously) for starting up, for example,

one need not cool down so much, orone can work at ordinary temperature with water cooling,-or according to the amount of-dilution, even without cooling, as the small rise in temperature which may then take place does not have such a detrimental effect, or one may heat to higher temperatures, evento V the condensing agent used.

It is to be understood that aceticacid as solvent. for the'acetylation may be wholly or partlylTeplaced by other suitable acids or sol vents, or that acetic acid or such otheracids or solvents may be partly replaced bysolvents or liquids such as chloroform or tetrachlorethanevor even diluents such as carbon tetrachloride', trichlorethylene, benzol, etc, so long as with such solvents, diluents ormiX- tures one is able togetla solution by acetylation; but the employment of such other solvents-or diluents is not'so advantageous as the use of acetic acid aloneas-solvent. Sol-.

vents or diluents that are capable of being converted into esters by means of fatty acid anhydridesare obviously unsuitable for vuse in this. present process. The solvents, or solvent mixtures above referred to mustbeemployed in such quantities as givean increased p The acetic anhydride of the applicants or greatly increased dilution of the esterification. mass. as compared with the quantity of acetic acid hitherto usually employed;

.as 25% and more calculated onthewei process'can be replaced other anhydrides of fatty acids to produce the corresponding cellulose esters. I r

If the acetylation is performed with larger I quantities of acetic anhydr de or with acetic anhydride alone, for example, ifinstead of taking acetic acid man-amount 8' times the weight of the cellulose, plus acetic anhydride in an amount 2% times the Weight of the cellulose, making :a total of 10 times liquor relatively to theweight of the cellulose, one takes acetici'anhydride alone in this total amount, one will observe that the acetylation solution so produced withstrongcondensing agents 1s relatively very thin; This however is less pronounced; whenmuch weaker con- (lensing agents are usedwhich may'even requiresomeheatin'g,especially if usedin small quantlty. I K

The finalfquality' of product obtained,

pecially' from a viscosity point of view, ac-

cordingly substantially improved by the use of weak condens ng agents instead of strongiconc'lensmg' agents when acet c anhydride isused insubstantial excess of the amount necessary for real acetylation. l/Vith sulphuric acid it seems that the acetic anhy- 'dride acts very quickly in adepolymerizing and degradingn anner on thecellulose. i

If acetic anhydride is used in abig excess,

phuric acid is completely neutralized to a salt, as 111' ammonium sulphate, n which case a higher temperature is usedfor acetylation and'the quantities of condensin agent are preferablysubstantially reduced. I v 'The best results however appear .to be obtained when the quantity of acetic 'anhydride is just that necessary for acetylation, or no slubstantialexcess,forexamplebetween about 1.5 and E}, andpreferablybetween about 1.8 and 2 times the weight of the cellulose, the

exact quantity being each time determined by the reaction, inasmuch as differences of humi dity in the cellulose and acetic v'anhy'd'ride percentage and percentage of acetic acid are best ascertained by the acetylation reaction. As shown by comparison of results, the products obtained with a minimum quantity of acetic anhydride are much more v-iscous Inasmuch as the reaction can be mastered much more easily, higher quantities of con-- densing agent, than usual can be employed i with much more ease, e. over 20%, such ght of the cellulose, though there is noadvantage n using larger quantities than 25%. On the other hand, the quantities ofi icondensifng .95 e, g. in amounts 4, 5 or 6 times the weight of it agent'canbe redueed to any smaller amounts, such. as 1Q%, 5%, 2% or lessl- V By varying the amount 1 of condensing ;agent,.--pr0duets with; different solubilities teria'ls are brought together or incorporated" in carrying-the inventioninto-zeifeet may be andother properties can be obtained. The

order or manner in which the respective mavariedin .any suitable or desired way.

v The reaction according to the'presentin- 'veiition' may {also be executedin suspension, in which] case the cellulose is preferably treated beforehandwith a mixture of the-increased quantity of acetic acid or corresponding; solvent or-gsol'vent mixtures containing the condensing agent, and afterwards intro jduced into a mixture of. the necessary quan Y tity of the acetic anhydride and a givennonsolvent diluent, like benzol or carbon tetra chloride or anyother; suitable diluentemployed in sutficient quantity to prevent solutionyof the cellulose.

E111 orderto speed up ther eaction the cellulose or cellulose conversion product mayreeelve a pretreatment with concentrated or ldilute'acetic" acid orother organic (fatty) acid .at fordinaryi temperature or with cooli ingorv at elevated'or even boilingtemperatunes. The acid, preferably, should contain small. quantities of sodium acetate or @Oilllfil suitable agents capable of neutralizing any mineral acid which maybe present,

since the latter 1 "would; have a destructive effecton the cellulosemolecule particularly when a. high temperaturei's used. The durati-on. of this treatmentand the temperatures *utilized'will depend on the acid used and its concentration. The details Y of this pretreatment are here omittedsinee; it ,formsthe subjeetmatterof-a divisional application.

. Thefollowing is anexample of the manner in which the process can be carried out but 160. "parts .thefinvention not to be considered as 'jlimitedto thisiexample- IfiExampZei," H by w eight of cellulose, for example cotton, are-introduced into a mixture "obtained by mixing SOOto 1200 parts by weight of glacialacetic acid, to parts b r-weightof sulphuric acid'and 6.5 m9 parts Sofa anhydrous sodium carbonate (or anequivalentfquantity of sodium acetate), and after- 'for-.- completing the reaction. The solution I SOQObtflilld-dS yustflas V scous, 1n sp te of the much greater dilution, as an acetylation-made chlo'ride orso forth. I

In the foregoing example, when 15 parts A with, less. dilution, and the acetylation product contained in it is consequentlymueh more viscous thanhitliertoknown. The product can'bejisolated and employed as suchorbe submitteditoa secondary or further treatment eitherin the original acetylation solu- ',tion-or.afterisolation therefrom. Theisolation of the product from the acetylation so- :lutionmaybe-effected by precipitating it in ,Wateror withdiluents such as carbon tetraof sulfuric acid are employed together with 6.5 parts ofsodium carbonate, the sodium carbonate reacts with 12 parts of sulfuric acid to form 14.5 parts'iof sodium bisulphate which contains?! parts of free sulfuric acid, so that the condensing agent used is a bisulphate containing about 20% of its weight of free sulfuric acid.

The reaction'goes more slowly in proportion as the quantity of condensing agent is reduced, and in such case more acetic anhydride may-be employed: a

The primary cellulose acetates obtained according to thepresent inventioncan either be used directly as such for, any technical purposes, like the manufacture of artificial silk celluloid-like masses, films, varnishes,

etc, especially when they are directlysolu ble in acetone or dilute acetone j or they. may be first submitted to axfurther or secondary treatment or. reaction either in the original esterification solution or after isolation therefrom, and either in solution or suspension.

Such further or so called secondary treatment may be along the lines indicated in my British Patents 20,977/1911, and 20,852/ 1912 or my U. S. Patents 1,217,722, and Reissue 14,338. Y I

.In these patents as referred tov I-have shown how the primary esterification products or other esterification solutions or otherwise made up solutions or suspensions of these products can be thustransformed by r using the direct acetylation solutions or other solutions or suspensions of the primary esterificationproduct, with or without the addition of water or other similarly acting agents having the effect of destroying the M acetic anhydride, and which at the same time should preferablybe able to be themselves csterified without producing water in any way, even intermediately," as for instance lactic acid (the absence of water in'thetreatment, or the quantity of water or similarly acting agents used directing the phases of solubilities passed through).

,More particularly the condensing agent may be neutralizedpartially or completely and the secondarytreatment may then be eflected, either zit-ordinary temperature or ata higher temperaturethatis to say, in the presence of freeorganic acids onlyyas ex- 4, lines 119, 120-129.

plained in my Ui'S. Patent-1,217,722, page Furthermore, as shown in my said patents the weaker the condensing agent the'more' Water or similarlyacting agents one can use in the secondary reaction for getting given phases of solubilities. I However, the use of' less Water or similarly actingagentsor no 'wateror similarly-acting agents maybe resorted to for passing through many more phases of solubilities more slowly'a'nd therefore more distinctly.

It is to be understood, however, that the various solubilities"developed in the sec- WVhat' I. claim Letters'Paten-t is e I 1. Processfor the manufacture of cel- .ondary reaction or treatmentof the products of the present invention do not necessarily correspondto those developedin the products obtained according 'to my said previous U.':S. *rei'ssue Patent 14,338 and Patents 1,278,885, 1,280,974 and 1,280,975 and my to the primary esterification products 013-.

tain-ed according to the present invention.

and desire to secure by lulose acetate, characterized in that the acety lati'onof cellulose is performed with acetic anhydride and a Weak condensing agent loseacetate, characterized in that the acetylawhich'isa'salt' of sulphuric 'acid'in presence of a quantity'of'an organic solvent, non-esterifiable by f t y acid anhydride over s times the'weight of the cellulose.

2. Process for the manufacture of cellulose'actate. characterized in that the acetylaof a we'ight of the cellulose. 1

oil

tionof cellulose is performed with acetic anhydride and a Weak condensing agent which is a. salt of sulphuric acid in presence quantity of acetic acid over 8 times the 3.'Processfor the manufacture of cellulose c acetate, characterized in that the acetylation of cellulose is performed with acetic anhydride and'a bisulphate in presence of a quantity of an. organic solvent non-esterifiable by acetic anhydride, over 8 times the weightof the cellulose.;."

4; Process for the acetate,c haracterized injthat the acetylation of cellulose: is performed with acetic anhydride and abis'ulphate in presence of a quanmy, of acetic acid. over 8 timesthe eight of the cellulose. V e

5. Process for themanufacture of cellulose acetate,characterized in that the acetylation of cellulose is performed with 1 acetic anhydride and a bisulphate containing a small proportion of free sulphuric acid in presence of a quantity of an organic solvent, nonesterifiable by acetic anhydride over 8 times the weight of the cellulose;

6. Process for the manufacture of cellulose manufacture of cellulose acetate,characterized iri'that the acetylation of cellulose is performed with aceticanhydrideand a b'isulphate containing-a small proportion of freesulphuric acid in presence of a quantity of acetic acid over- 8 times the Weight of the cellulose. I

7. Process for the manufacture of cellulose acetate, characterized in thatthe acetylation of cellulose is performed with acetic anhydride and 'a weak condensing agent in presence of a quantityjiof acetic acid over about 12'tirnes the-weight of thecellul ose.

8. Process for the manufacture of cellulose acetate, characterized in that the'acetylation of cellulose is'perforrned with acetic anhydride anda weak condensing agent iii-pres- :ence "of a quantity of acetic acidover about 15't1mes theweight of the cellulose.

9. Process for the manufacture'of cellulose acetate, characterized inthat the acetylation of cellulose is performed with'acetic anhydride and a Weak condensing-agent which is a salt of sulphuricacidin presence of a quantity of acetic acid over about 12 times the weight of=the cellulose. I I 7 10. Process for the manufacture of cellulose acetate, characterizedin that theacetylation of cellulose isperfo'rmed with-acetic anhydride'and a bisulphate in presenceof aquantity of acetic acid over about 12 times the Weight of the-cellulose. V v

glltProcess for the manufacture of cellution of cellulose is performed with acetic anhydride and a'bisulphate inpresence of a quantity of acetic acidover 8 times the weight of the cellulose, under such conditions that the temperature doesnot 'riseabove about C. during acetylation. 7

12. Process for the'manufacture vof cellulose acetate, characterized in that the a cetylation of cellulose is'performed with acetic anhydride and a bisulphate containing a small quantity of free sulphuric acid in presence of a quantity of acetic acidlover ,8 times the Weight of the cellulose, the acetylation being conducted with water cooling so that the temperature does not rise above about 35 C.

during acetylation;

13. Process accordingto'claim 5, characterized by the acetylation being conducted withwater cooling so that the temperature quantity of acetic acid over 8 times the weight of the cellulose, and the resulting cellulose presence of an acetic Vanhydridedestroying agent to modify the solubilitycharacteristics thereof. A

with heating to acetate is subjected to further treatment in a la -Process for the manufacture ofcel lu- I lose acetate, characterized in that the acety-" Y lation of cellulose is performed with acetic anhydride and a bisulphate' containing a small proportion of free sulphuric acid in presence of a quantity of acetic acid -over8 times the Weight of the cellulose, the acetyla tion being started at at'emperfaturebetween aboi1t0 C. and ordinary temperature. a

. 16. Process for the manufacture of cellulose acetate, characterized in that the acetylatlire being pre-cooled to, below ordinary temtion ofcellulose is performedwith aceticanhydride anola bisulphate containingasmall proportion of free sulphuric acid in presence.

of a quantity of acetic acid over 8 times the eight of the cellulose, the acetyla-tion mixperature and the temperature not exceeding about CI during acetylation.

In testimony whereof I have hereunto sribscribed my name.

HE RY DREYFUS. v V 

